Lubricating base oils used in the formulation of engine lubricants and industrial oils may be prepared from suitable hydrocarbon feedstocks derived during the refining of crude oil.
In the conventional manufacture of lubricating base oils, the residue remaining after the atmospheric distillation of crude oil (often referred to as "long residue") is further refined using vacuum distillation techniques. Typical products of the vacuum distillation are spindle oil, light machine oil, medium heavy machine oil and a residue (often referred to as "short residue"). A typical process for the preparation of lubricating base oils includes subjecting the spindle oil, light machine oil and medium heavy machine oil to further processing in which undesired aromatic compounds are removed by solvent extraction using furfural or phenol as the solvent. The resulting fractions are then subjected to a catalytic treatment in the presence of hydrogen, after which the fractions are subjected to a dewaxing operation to yield the final lubricating base oil. The short residue may be subjected to a deashpalting treatment and the resulting hydrocarbon stream used as a feed for the aforementioned catalytic treatment.
During the catalytic treatment, the hydrocarbon feed is contacted with a suitable catalyst in the presence of hydrogen. Typical reactions occurring during this treatment are hydrogenation reactions, hydrodesulfurization, hydrodenitrogenation, and some hydrocracking, yielding lower molecular weight hydrocarbons. Most importantly, however, wax molecules in the feed are subjected to hydroisomerization reactions, leading to lubricating base oils having improved viscometric properties, in particular higher viscosity indexes. An ideal catalyst for use in the catalytic treatment would promote the hydroisomerization reactions, while minimizing the hydrocracking reactions, thereby resulting in a lubricating base oil having a desirable viscosity index in a high yield.
Catalysts suitable for use in the catalytic treatment combine a hydrogenation component and an acid component. Suitable catalysts are known in the art. For example, most suitable catalysts for use in this treatment are disclosed in British Patent Nos. 1,493,620 (GB 1,493,620) and 1,546,398 (GB 1,546,398). GB 1,493,620 discloses a catalyst comprising nickel and tungsten as hydrogenation components, supported on an alumina carrier. GB 1,546,398 discloses a catalyst comprising, as a hydrogenation component, nickel and/or cobalt in combination with molybdenum, supported on an alumina carrier. In both GB 1,493,620 and GB 1,546,398 the required acidity for the catalyst is provided by the presence of fluorine.